*{
  margin: 0; 
  padding: 0;
}

*{
  box-sizing: border-box;
}
*::before{
  box-sizing: border-box;
}
*::after{
  box-sizing: border-box;
}

.html-mode {
  animation: flip 2s;
}
  
@keyframes flip {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}